The invention relates to a process for passing carbon dioxide through a cased, cemented and perforated well. Carbon dioxide in the presence of moisture leads to carbonic acid attack of oil well cement. This attack, if allowed to proceed unchecked eventually weakens the cement to an unacceptable condition. The major constituent of set cement, hydrated calcium silicate, breaks down by the action of CO.sub.2 as follows: EQU 3CaO.2SiO.sub.2.3H.sub.2 O+3CO.sub.2 .fwdarw.3CaCO.sub.3 +2SiO.sub.2 +3H.sub.2 O.
The reaction products calcium carbonate and silica possess less binding power than hydrated calcium silicate. Therefore, a considerable deterioration in cement strength takes place by CO.sub.2 attack.
Cement is exposed to CO.sub.2 in wells for injection of CO.sub.2 and in those used for the production of reservoir fluid which, at a certain stage of a CO.sub.2 -flooding project, contains CO.sub.2 as well. Also in source wells, used for the supply of CO.sub.2, there is exposed cement.
The only place of exposure of CO.sub.2 in injection, production and source wells is at the perforations, where the perforation tunnels traverse the cement sheath between casing and borehole. To maintain the integrity of injection, production, and source wells, the exposed cement should be shielded from CO.sub.2 attack. This can be achieved by providing the exposed cement with an impermeable layer of inert material which protects the cement. It has now been found that nickel is very suitable for this purpose.
Electroless metal plating has been used for consoliation of loose or incompetent subsurface formations. U.S. Pat. No. 3,393,737 describes an electroless metal plating technique for consolidating loose formations, and discloses that this technique is superior to resin consolidation techniques. U.S. Pat. No. 3,685,582 describes an electroless metal plating technique for consolidating loose formations which can be advantageously used in high temperature formations (250.degree. to 400.degree. F.).